Since peptides tend to be easily denatured due to their low stability, degraded by in-vivo proteolytic enzymes, thus losing the activity, and have a relatively small size, thereby easily passing through the kidney. Accordingly, in order to maintain the blood level and the titer of a medicament comprising a peptide as a pharmaceutically effective component, it is necessary to administer the peptide drug frequently to a patient to maintain desired blood level and titer. However, the peptide drugs are usually administered in the form of injectable preparations, and such frequent administration for maintaining the blood levels of the physiologically active peptides cause severe pain for the patients. To solve these problems, many efforts have been made. As one of such efforts, there has been suggested an approach that transmission through the biological membrane of the peptide drug is increased, and then the peptide drug is transferred into the body by oropharyngeal or nasopharyngeal inhalation. However, this approach is still difficult in maintaining the in-vivo activity of the peptide drug due to the remarkably lower in-vivo transfer efficiency, as compared with injectable preparations.
On the other hand, many efforts have been made to improve the blood stability of the peptide drug, and to maintain the drug in blood at a high level for a prolonged period of time, thereby maximizing the pharmaceutical efficacy of the drug. The long acting preparation of such peptide drug therefore is required to increase the stability of the peptide drug, and to maintain the titers at sufficiently high levels without causing immune responses in patients.
As a method for stabilizing the peptide, and inhibiting the degradation by a proteolytic enzyme, some trials have been performed to modify a specific amino acid sequence which is sensitive to the proteolytic enzyme. For example, GLP-1 (7-37 or 7-36 amide), which functions to reduce the glucose concentration in blood for the treatment of Type 2 diabetes, has a short half-life of the physiological activity of about 4 minutes or less (Kreymann et al., 1987), due to loss of the titers of GLP-1 through the cleavage between the 8th amino acid (Ala) and the 9th amino acid (Asp) by a dipeptidyl peptidase IV (DPP IV). As a result, various investigations have been made on a GLP-1 analog having resistance to DPP IV, and trials have been made for substitution of Ala8 with Gly (Deacon et al., 1998; Burcelin et al., 1999), or with Leu or D-Ala (Xiao et al., 2001), thereby increasing the resistance to DPP IV, while maintaining its activity. The N-terminal amino acid His7 of GLP-1 is critical for the GLP-1 activity, and serves as a target of DPP IV. Accordingly, U.S. Pat. No. 5,545,618 describes that the N-terminus is modified with an alkyl or acyl group, and Gallwitz, et al. describes that His7 was subject to N-methylation, or alpha-methylation, or the entire His is substituted with imidazole to increase the resistance to DPP IV, and to maintain physiological activity. Whereas the resistance to dipeptidyl peptidase is increased to improve its stability, the His7-modified derivatives are found to have markedly reduced receptor affinity with lower cAMP stimulation at the same concentration (Gallwitz. et al., Regulatory Peptide 79:93-102 (1999), Regulatory Peptide 86:103-111 (2000)).
In addition to GLP-1, exendins are peptides that are found in the venom of glia monster, a lizard common in Arizona and Northern Mexico. Exendin-3 is present in the venom of Heloderma horridum, and exendin-4 is present in the venom of Heloderma suspectum. The exendins have a high homology of 53% with GLP-1 (Goke, et al., J. Bio. Chem., 268:19650-55 (1993)). Exendin-4 reportedly acts at GLP-1 receptors on specific insulin-secreting cells, at dispersed acinar cells from guinea pig pancreas, and at parietal cells from stomach, and the peptide is also said to stimulate somatostatin release and inhibit gastrin release in isolated stomachs. In addition, exendin-3 and exendin-4 were reportedly found to stimulate cAMP production in pancreatic acinar cells, and to stimulate amylase release from pancreatic acinar cells. Since the exendin-4 (U.S. Pat. No. 5,424,686) has a sequence of His-Gly, instead of His-Ala which functions as a substrate of dipeptidyl peptidase in GLP-1, it has resistance to DPP IV, and higher physiological activity than GLP-1. As a result, it had an in-vivo half-life of 2 to 4 hours, which was longer than that of GLP-1. Although the native exendin has an in-vivo increased half-life than GLP-1, its physiological activity is not sufficiently sustained. For example, in the case of a commercially available exendin-4 (exenatide), it needs to be injected to a patient twice a day, which is still difficult for patients.
To improve therapeutic efficacy of the native exendin, trials have been made to prepare its analogs, derivatives and variants. The term “analog or variant” typically refers to a peptide prepared by substitution, deletion or insertion of one or more amino acids into or from the native peptide. The term “derivative” refers to a chemically modified peptide, prepared by alkylation, acylation, esterification, or amidation of one or more amino acids in the native peptide.
Novel exendin agonist compounds are described in PCT Application No. PCT/US98/16387. Claiming priority thereon, a method for reducing food intake using exendin is disclosed in U.S. Pat. No. 6,956,026. In addition, claiming priority on the PCT application, use of exendins and analogs thereof for the reductions of food intake is disclosed in EP0996459, and exendin agonist compounds are disclosed in U.S. Pat. No. 7,157,555. However, they merely disclose several sequences of exendin analogs. Moreover, there is no mention of activity and property with respect to said analogs, which is also not supported by the detailed description.